This invention pertains to fuel combustion furnaces, and more particularly to normalizing furnaces suitable for use with high pressure combustion air and high velocity flue gas.
The normalizing furnaces of the prior art rely primarily on radiant heating and only secondarily upon forced convection. Since the rate of heat transfer by radiation is fixed, the heat transfer per time is also limited in such prior art furnaces. Where prior art furnaces operate at low pressures and velocities, the heat treat time for a given work piece is extended thereby substantially increasing fuel consumption.
Prior art burners are extremely complex and have many parts. Also, a large pressure drop occurs between the air blower and burner. Such a pressure drop is necessary in prior art burners to permit adequate control. The burners of the prior art are not able to achieve the small combustion chamber space and air/gas mixture of pre-mix systems.
Many high velocity burners operate with excess air and therefore require an auxiliary air source not regulated by the regulator for the air/gas mixture whereby as the air/gas mixture is turned down, such burners become oxidizing and therefore an excess air burner.
Most prior art systems have relatively low combustion chamber pressures as compared to the present invention. The burner of the present invention operates at increased air pressure to permit combustion chamber pressures of approximately 8 to 10 times greater than that generally achieved by the prior art.
Further, the prior art furnaces using high velocity burners, the combustion chambers have round exit ports which prevent the entire surface area of the work piece from being exposed to the hot flue gases. The hot flue gases leaving the exit ports tend to heat the work piece in a "ribbon" manner, i.e., that portion of the work piece exposed to the exit ports as the work piece rotates and travels through the hearth. This prevents uniform heating of the work piece.
The present invention overcomes these defects in the prior art. Other objects and advantages of the invention will appear from the following description.